qtop: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/qtop - from package: qtop

You may install the required package with command apt-get install {package}
Error in other languages:
qtop: bevel nie gevind nie
qtop: comandă negăsită
qtop: comando não encontrado
qtop: commande introuvable
qtop: command not found
qtop: käsku ei ole
qtop: không tìm thấy lệnh
qtop: komanda nerasta
qtop: Kommando nicht gefunden.
qtop: kommandot finns inte
qtop: komut yok
qtop: nie znaleziono polecenia
qtop: níor aimsíodh an t-ordú
qtop: no se encontró la orden
qtop: no s'ha trobat l'ordre
qtop: opdracht niet gevonden
qtop: parancs nem található
qtop: perintah tidak ditemukan
qtop: príkaz nenájdený
qtop: příkaz nenalezen
qtop: команда не найдена
qtop: командата не е открита
qtop: 命令找不到
qtop: コマンドが見つかりません